TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3390 SUBJECT: Keck/DEIMOS Spectrum of Possible Host Galaxy for GRB050509b DATE: 05/05/09 09:22:11 GMT FROM: Josh Bloom at Harvard/CFA J. X. Prochaska (UCO/Lick), M. Cooper (UCB), J. Newman (LBNL), J. S. Bloom (UCB), K. Hurley, (SSL/UCB), C. Blake (Harvard), B. Gerke (UCB), and H. W. Chen (MIT) report: "We have acquired a DEIMOS longslit spectrum of the galaxy at ra 12:36:12.90, dec +28:58:58.8 (J2000) (=2MASS 2MASX J12361286+2858580) which is tentatively identified as the host of GRB 050509b. We measure a redshift of z=0.226 based on Ca H and K absorption and numerous other absorption features. We do not detect any significant emission at Hbeta, Halpha or [O II]. The spectral features are consistent with an early type galaxy with no ongoing star formation. If the association is confirmed, this would be the first GRB host that is an early-type, hinting that GRBs of short duration may be due to progenitors that are unrelated to current and on-going star formation. This notice may be cited."